题目：

Given a digit string, return all possible letter combinations that the number could represent.

A mapping of digit to letters (just like on the telephone buttons) is given below.

Input:Digit string "23"

Output: ["ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"].

Note:

Although the above answer is in lexicographical order, your answer could be in any order you want.

题意：

给定一个数字字符串，返回这个数字能代表的全部的字母的组合。

数字对字母的映射例如以下图所看到的（就在电话的按键中）

Input:Digit string "23"

Output: ["ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"].

返回的结果能够依照随意的顺序。

算法分析：

* 思路:





 *比方“234”这个字符串，我能够先将0...1的全部排列找到-->{"a", "b", "c"}





 *再进一步将0...2的全部排列找到-->{"ad", "ae","af", "bd", "be", "bf", "cd", "ce", "cf"}





 *如此循环...直到字符串末尾。实现例如以下

AC代码：

public class Solution

{

    public  ArrayList<String> letterCombinations(String digits)

    {

    	ArrayList<String> res=new ArrayList<String>();

    	String charmap[] = {"0", "1", "abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz"};

    	if (digits.length()==0) return res;

    	res.add("");

        for (int i = 0; i < digits.length(); i++)

        {

          ArrayList<String> tempres=new ArrayList<String>();

          String chars = charmap[digits.charAt(i) - '0'];

          for (int c = 0; c < chars.length();c++)

          {

            for (int j = 0; j < res.size();j++)

              tempres.add(res.get(j)+chars.charAt(c));

          }

            res = tempres;

        }

        return res;

    }

}